1. Field of the Invention
The present invention relates to mixers used in a millimeter wave band and a microwave band, radar modules, and communication apparatus incorporating the same.
2. Description of the Related Art
As a conventional mixer, Japanese Unexamined Patent Application Publication No. 10-75109 describes a mixer having a structure in which a diode is mounted in a non-radiative dielectric line (NRD guide).
In the above structure, a dielectric strip and a circuit board are arranged between two substantially parallel conductive plates to form a dielectric line. The conductive plates and conductive patterns on the circuit board constitute suspended lines. Additionally, the conductive patterns of the suspended lines are disposed in a direction crossing substantially perpendicularly to the dielectric strip, and also there are arranged filter circuits coupled with the dielectric line to block signals propagating through the suspended lines at at least two parts of the conductive patterns of the suspended lines sandwiching the dielectric strip so that a resonant circuit is provided. A diode is mounted in series to the conductive patterns inside the resonant circuit.
However, between the filter circuits composed of stubs of the suspended lines, a signal does not necessarily produce resonance. Thus, high frequency energy leaks from the filter circuits composed of the stubs and the like. This causes loss. In addition, due to the suspended lines having a low Q, the entire loss increases.
Accordingly, it is an object of the present invention to provide a mixer capable of achieving loss reduction, a radar module, and a communication apparatus incorporating the mixer and having high efficiency.
According to a first aspect of the invention, there is provided a mixer including a dielectric substrate, electrodes having apertures, the electrodes being formed on both main surfaces of the dielectric substrate such that the apertures are opposed to each other via the dielectric substrate, two conductive plates arranged substantially in parallel, the dielectric substrate being disposed between the conductive plates to constitute a planar TE-mode dielectric resonator, a slit formed between the electrodes on a main surface of the dielectric substrate to be continuous with one of the mutually opposing electrode apertures, and a diode connected manner bridging the slit.
With this arrangement, an input signal is received by the planar TE-mode dielectric resonator and applied to the diode bridging the slit. Accordingly, a mixing signal is extracted from the electrodes to which both ends of the diode are connected.
According to a second aspect of the invention, there is provided a single balanced mixer including a dielectric substrate, electrodes having apertures, the electrodes being formed on both main surfaces of the dielectric substrate such that the apertures are opposed to each other via the dielectric substrate, two conductive plates arranged substantially in parallel, the dielectric substrate being disposed between the conductive plates to constitute a planar TE-mode dielectric resonator, slits formed on both main surfaces of the dielectric substrate and opposed to each other via the dielectric substrate to be continuous with the electrode apertures, and diodes connected bridging the slits. With this arrangement, the single balanced mixer using the two diodes can be formed.
In addition, the mixer according to one of the first and second aspects may further include electrode separating portions formed to separate the electrodes to which both terminals of at least one of the diodes are connected, so that a direct current does not flow through the electrodes. With this arrangement, since a bias voltage can be applied to the at least one of the diodes from an external power source and thereby the diode can be driven at an optimum driving point, loss in the mixer can be reduced.
In addition, each of the electrode separating portions may be formed at a position where the intensity of an electric field is high in the planar TE-mode dielectric resonator. With this arrangement, the effect of reducing conductive loss can be enhanced.
In addition, the electrode apertures may be rectangular-shaped, and therefore the dielectric resonator may be a rectangular planar TE-mode dielectric resonator. With this arrangement, the formation of electrode patterns can be facilitated. Furthermore, a dielectric resonator having a high Q, which is capable of suppressing the occurrence of a spurious mode, can be formed on the dielectric substrate having a limited area.
In addition, the mixer of the invention may further include a dielectric strip arranged between the two conductive plates to form a dielectric line, which is coupled with the TE-mode dielectric resonator and is used as a signal-input line. This arrangement enables the easy formation of a mixer incorporated in an apparatus using a dielectric line as a transmission line.
According to a third aspect of the invention, there is provided a radar module including the mixer of the invention. The mixer is disposed in a circuit section mixing a received signal with a local signal. With this arrangement, the radar module can obtain high efficiency to improve detection capabilities.
According to a fourth aspect of the invention, there is provided a communication apparatus including the mixer of the invention. The mixer is disposed in a circuit section mixing one of a received signal and a transmitted signal with a local signal. With this arrangement, while reducing loss, frequency conversion can be performed to obtain high sensitivity.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.